The present invention pertains to improved ossicular prostheses. More particularly, the present invention pertains to bendable ossicular prostheses which can be shaped and sized to conform to the spacing in the middle ear of a person requiring such a prosthesis and which can be implanted in the middle ear without the necessity for an interfacing layer of human tissue.
The middle ear is an irregular, air filled space within which three auditory ossicles provide mechanical linkage between the tympanic membrane or ear drum and the opening to the inner ear, commonly referred to as the oval window. The three auditory ossicles are the malleus, the incus, and the stapes. The malleus includes a handle portion and a head portion. The handle portion contacts the tympanic membrane. The stapes includes an arch, having a pair of limbs, and a footplate. The footplate communicates with the oval window leading to the inner ear. The incus couples vibrations from the head portion of the malleus, caused by the malleus handle portion vibrating due to sound impinging on the tympanic membrane, to the arch of the stapes. The stapes footplate passes these sound vibrations to the inner ear. The lever action of the ossicles within the middle ear causes amplification of the sound vibrations, with the result that a greater vibrational force is experienced at the oval window than at the tympanic membrane.
Unfortunately, a number of middle ear conditions can result in damage to one or more of the ossicles, causing partial or total hearing loss. Various prostheses have been developed as replacements for the ossicles. One of the earliest such prostheses is a porous polyethylene strut. However, this device requires that a piece of cartilage, harvested from the patient at the time of the ear surgery, be positioned between the tympanic membrane and the head of the prosthesis. Treace, U.S. Pat. No. 4,510,627 shows an ossicular prosthesis having a porous body of a biocompatible material, such as polyethylene, surrounding an inner core of a biocompatible metallic material, such as stainless steel. The body has an enlarged head, which contacts a piece of human tissue that abuts the tympanic membrane, and a shaft, which contacts the stapes or the footplate of the stapes. The angle at which the shaft extends from the head can be varied, and the shaft itself can be bent to permit the device to adapt to various inner ear geometries. Nevertheless, the necessity for a human tissue interface between the head of the prosthesis and the tympanic membrane is a significant handicap in the use of such a prosthesis.
Another recently available ossicular prosthesis has a porous polyethylene head molded around a coiled wire, with the distal end of the wire extending from the head and inserted straight into a shaft of porous polyethylene or of Teflon. When this device is bent or adjusted, the wire can, unknown to the surgeon, migrate through the polyethylene shaft or head. As a result subsequent implantation in the middle ear could have hazardous results.